SA: Bank & Building society interest tax and Income Tax due

[goodraw]

I wonder if anyone can explain why my total tax due as a sole trader on my tax return ( which I'm not querying), is reduced by the tax thats been deducted on (some) of my savings in building soc; accounts;
Even though my taxable income is lower this year than last; "the interest received from banks etc" last year was over £6000, this year its just over £2000. The " minus tax deducted figure" last year was £ 1200, but this year its only £ 200, making my final tax liability higher this year than last!?
Any info gratefully received.

[maths]

Income tax at source is deducted from bank interest at the 20% rate; this would be the amount of income tax credited against your initial tax liability on your total income less personal allowances etc.

On £2000 of interest this would be £400 not £200.

Has any interest been credited "gross" by the banks which would reduce income tax deducted at source?

[maths]

Alternatively, only £200 was necessary to deduct to reduce your tax payable to nil; giving a tax refund of £200.

[goodraw]

Dear Maths, thank you for your reply, I am re-checking my accounts to find out if they all have had tax deducted at source; I will post again once I've done this. Its beginning to make sense...

[goodraw]

Hi, Re-checked the figures and it appears that I received all interest with tax deducted, which was £1757; if I dont put the actual figures in for tax deducted, can hmrc automatically work out the correct ammount?